Automated fluid injection devices, particularly automated needle syringes, have gained wide acceptance by industry, universities, and by the scientific and medical communities. This is due in large part to the advantages offered by modern data gathering techniques, and consequent reduction in operating manpower without loss in accuracy.
In the operation of automated fluid injection devices generally, septum covered vials are charged with a fluid specimen and transported in seratim via a magazine to a station adjacent a probe assembly, the probe assembly is projected through the septum of a vial and employed as a conduit to convey a portion of the fluid specimen to the syringe. Within the barrel of the syringe, a quantity of the fluid specimen is measured out and injected via the dispensing end of the syringe into the inlet of the analytical instrument.
Automated fluid injectors are capable of dispensing very small, accurately measured quantities of fluid specimens on the order of a few microliters, generally up to about 10 microliters with high accuracy and precision. When the barrel of a syringe is of quite small inside diameter, generally on the order of about 0.5 millimeter (mm) to about 1 mm inside diameter, the fluid specimen can be loaded into the bore of the syringe such that it is completely filled, without displacement of any portion of the fluid therein by gas or air. When the bore of the syringe can be loaded in this manner a preselected, predetermined amount of the fluid specimen can be displaced from the bore of the barrel with extremely high precision and accuracy. When however the bore of the barrel is greater than about 1 mm in diameter, gas or air often enters into the bore with the fluid specimen, this producing small bubbles or foam which can drastically interfere with the accuracy and precision of such types of automated fluid injector. Albeit the length of the syringe bore can be increased, and the diameter of the bore decreased accordingly to provide the space required for larger volumes of a fluid specimen, this means of decreasing the bore diameter of syringes obviously has serious limitations. Among other reasons, there are some very practical limits in employing syringes of great length, from both the operation and manufacturing point of view. Generally, it is undesirable to build syringes the barrels of which are of length greater than about 60 mm. There is thus a need for automatic fluid injectors capable of employing syringes having barrels with bores with relatively large diameter, and of relatively short length, particularly syringes having barrels with bores of about 1 mm, and greater, into which fluid specimens can be loaded without the presence therein of any significant amount of gas, or air as bubbles, or foam.